This invention relates to an initializing circuit for an electronic calculator or computing system.
In electronic logic systems such as calculator circuits an initializing circuit is essential at power turn-on to provide a pulse of a duration sufficient to reset the system to the appropriate rest state, that is, to initialize all the relevant storage elements in the system so that they are ready to perform their logic functions in the proper manner. Moreover, this initializing pulse must do this every time the calculator system is turned on, and only for a reasonable period of time following the appearance of viable power supplies. Once generated to perform its initializing function, it must shut off and stay off so as not to interfere in any way with the regular operation of the system.
Fundamentally, the problem of providing a useful initializing pulse circuit involves the problem of how to generate the pulse and also of determining when to generate it. The latter factor requires a capability of sensing when the power comes on. This problem is aggravated when the circuit is energized by two power supplies having variable rise times.
Experience, particularly with low cost calculators, has shown that an initializing circuit must tolerate power supply rise times of at least up to 0.5 msec. and sometimes up to 20 msec. or possibly more. It must tolerate noisy power supplies on turn-on, and it must not impose special sequencing on the power supplies when more than one supply is required. A general object of the present invention is to provide an initializing circuit that solves the aforesaid problems.
Another more specific object of the present invention is to provide a power-on initializing circuit for an electronic logic circuit that is capable of handling relatively long power supply rise times; that is capable of fast recovery on turn off/turn on; that is independent of power supply sequencing when two power supplies are used; and that is immune to noise on turn-on with a single power supply and is also immune to noise on turn-on of two power supplies provided that the two power supplies track.
Still another object of the present invention is to provide an initializing circuit for an electronic calculator particularly adaptable for implementation as an integrated circuit semiconductor device of the MOS (metaloxide-silicon) type utilizing both enhancement mode and depletion mode transistor devices and one that minimizes the use of unorthodox circuit elements.
Another object of the present invention is to provide a power-on initializing circuit for an electronic logic circuit that is capable of producing an initializing pulse of a minimum of one or more bits of delay or of using a one bit of delay to a wider initializing pulse, where necessary.
Yet another object of the present invention is to provide an initializing circuit that is particularly adaptable for use in small, one-chip electronic calculators.